Aluminum and aluminum alloys are desirable manufacturing materials across many industries. When processing aluminum and aluminum alloys, care is taken to remove naturally occurring layers of oxidation (e.g. aluminum oxides) that develop on exposed aluminum and aluminum alloy surfaces. Such removal of aluminum oxide layers can desirably lower surface resistivity to, for example, facilitate welding, facilitate or enhance adherence of later-applied protective coatings, enhance anodizing or conversion coating, and/or facilitate other aluminum and/or aluminum alloy processing, etc.
Solutions used to dissolve or otherwise ameliorate the undesirable effects of oxidation on aluminum and aluminum alloy surfaces are referred to as deoxidizing solutions or cleaning solutions. Such deoxidizing solutions are typically strongly acidic, and not only remove the oxide layer, but also attack the base metal surface under the oxide layer to a certain extent. Since many aluminum alloys comprise copper, some of the copper will be dissolved along with the oxide layer. If the copper ion concentration is allowed to rise to, or above, certain levels, some of the copper may redeposit onto the aluminum workpiece being deoxidized. Such layers of redeposited copper are referred to as “smut”.
Such smut layers must be removed via desmutting processes to obtain aluminum and aluminum alloy workpieces in desired processing condition, as copper smut interferes with further aluminum processing stages including, without limitation, uniform aluminum protective coatings, aluminum coatings applied to aluminum workpieces for purposes of improving adhesion of subsequent coatings and treatments, etc.
Various agents and processes are known for smut removal, also known as “desmutting” operations. However, when the smut is removed, the copper ions and compounds are retained in the deoxidizing solution used to desmut the aluminum, requiring the eventual replacement of large amounts of desmutting solution from desmutting tanks and cleaning of the tanks. For example, such desmutting tanks may contain from about 30,000 gallons to about 50,000 gallons, or more. Replacement of such amounts of desmutting solution with regularity is time-consuming and expensive, not only in terms of the cost of replenishing the solution, but also in terms of waste, storage, removal and other costs associated with changing out the desmutting solution. Further costs are realized with respect to environmental concerns, as well as the adverse production impact caused by processing lines being shut down or otherwise interrupted from days or weeks while old aluminum desmutting solution is removed and replenished with new aluminum desmutting solution.